As an example of dried solid media, a dried solid medium is conventionally known which is prepared by lyophilizing a medium poured into a plastic dish and solidified (JP 60-19988B, referred to as “Prior art 1” hereinafter).
Further, there is also a known dried solid medium in the form of a film, which contains a gelling agent such as agar and is easily substantially restored to a previous state before it is formed into film by adding sterilized water (JP 6-311880A, referred to as “Prior art 2” hereinafter).
However, these conventional materials have the following problems.
Prior art 1 and Prior art 2 mentioned above are used in order to improve storage stability of media and the media are dried so that a water content in the compositions of finally obtained solid medium becomes 50% or less. Therefore, they have a problem that they require a long period of time as long as about 3 hours for full restoration of the media upon use.
Further, since the dried solid media obtained according to the aforementioned conventional techniques require a long period of time for restoration as described above, restoration in a relatively short period such as 1 to 10 minutes results in insufficient restoration. If such media are used for microorganism tests, growth of Staphylococcus aureus ATCC 6538P, Bacillus stearothermophilus var. calidolactis NIZO C953 etc., which are important bacterial species in microorganism tests of foodstuffs and so forth, is partially inhibited due to the insufficient restoration of the medium, resulting in inaccurate measurement of the number of microorganisms, as demonstrated by the Test Examples mentioned later.
That is, the conventional dried solid media have a problem that they require a long period of time for restoration, and thus they are not suitable for quick and accurate measurement tests of microbial numbers.
Further, it is known that a solid medium is dried in order to remove excessive moisture on its surface after its production. Since this drying process removes a part of solvent water from the solid medium prepared in a prescribed composition, water content of the medium upon actual culture of microorganisms should significantly differ from the prescribed content in the composition identifying the solid medium. Influences of medium-drying on the culture of microorganisms cannot be ignored. For example, it is known that growth of microorganisms is sometimes degraded due to drying etc., even when a medium is stored in a test tube with a cotton plug for several weeks. Moreover, uncontrolled removal of water sometimes makes the composition of solid media inconstant. Therefore, reproducible and accurate results may not be obtained in culture tests of microorganisms, especially those of microorganisms that are likely to be affected by the water content of medium.